Method of producing insulated magnet wire



April 3, 1951 +1. SAUMS 'ET AL 2,547,047

METHOD OF PRODUCING INSULATED MAGNET WIRE Filed May 22, 1947 3Sheets-Sheet 1 April 3, 1951 H. L. SAUMS ETAL METHOD OF PRODUCINGINSULATEDMAGNET WIRE 3 Sheets-Sheet 2 Filed May 22, 1947 A W. G. WIRESIZE 0 0 a w 2 mPDZZZ mum .rmmm awman O2 OU A.W. G. WIRE SIZE S m m S Rw M m w M Y NRN R A m H BY A??o RNEYs i @rmq April 1951 H. L. SAUMS ETAL2, 47,047

METHOD OF PRODUCING INSULATED MAGNET WIRE Filed May 22, 1947 s Sheets-Sheet s INVENTORS HARRY L. SAU MS JOHN H. V 1i HOWARD vW.STURGIS ATTORNEJS Patented Apr. 3, 1951 METHOD OF PRODUCING INSULATED MAGNET WIRE HarryL. Saums, John H. Vail, and Howard W.

Sturgis, Muskegon, Mich., assignors to Anaconda Wire and Cable Company,a corporation of Delaware Application May 22, 1947, Serial No. 749,804

4 Claims.

This invention relates to insulated wire, particularly wire of thecharacter known to the trade as magnet wire. The invention provides animproved method for producin such insulated wire, and novel apparatus inwhich the method of the invention may be carried out. Wire produced inaccordance with the invention is a new product possessing improvedcharacteristics, and. the wire is itself therefore included within thescope of the invention.

A common type of magnet Wire consists of a metallic wire having aninsulating enamel coating. Methods heretofore known for producing suchwires involve applying to the wire a number of coats of oleo-resinenamel, or some similar enamel, and baking the wire after applying eachcoat to dry and harden the enamel on the wire. The baking step hasalways been necessary in the commercial production of enameled magnetwires, because the only enamels heretofore successfully employed havebeen of the type requiring evaporation of solvent, with or withoutoxidation of the vehicle, to dry and harden the enamel film on the wire.The film produced by only one coat of these baked enamels is so thin astobe inadequate for electrical insulating purposes, and accordingly ithas been commercial practice to apply a minimum of three coats andsometimes as many as twelve coats, with a baking step intermediate theapplication of each coat. The need for applying a number of coats ofenamel has the effect, of course, of diminishing the amount of finishedwire that can be produced per unit of time with a given amount ofwire-enameling equipment.

Production of enameled wire by heretofore known methods is a slowprocess for still another reason. The drying and hardening of each coatof enamel requires baking for an appreciable length of time. There is apractical limit to the size of enameling ovens that can be built andoperated economically, and even in ovens of the largest size deemedpractical the rate at which" the wire can be passed therethrough, andstill allow adequate time for baking the enamel coat,

is lowvarying say from about feet per minute for No. 10 A. W. G.(American Wire Gauge) wire to about 55 feet per minute for No. 39 A.W.G.

In order to obtain maximum production from an lenameling oven, it mustbe operated at the highest temperature consistent with the maximumtemperature the enamel can withstand without deterioration (in order topermit passage of the wires through the oven at the greatest possiblespeed), and the wires must be closely spaced in the oven. Thus,enameling ovens are generally operated at a temperature of about 300 to360 C., and the wire spacing is about one-half inch. If the enameledwire is allowed to remain in the oven under these conditions for aperiod of time only slightly exceeding the normal baking time, dueeither to a variation in wire speed or toa break in the wire, theresulting overbaking will cause such deterioration of the enamel coatingas to make the wire valueless. A high degree of skill is required of theoperators of such ovens to avoid any such damage to the wire and toinsure the production of long lengths of uniformly baked enameled wiresuitable for use in the electrical trade.

We have discovered that insulated magnet wire of excellent quality canbe produced by passing a wire through a gelable lacquer maintained atabove its gelation temperature, and cooling the lacquer coated wirerapidly upon. its withdrawal from the lacquer to a temperature below thegelation temperature of the lacquer. The resulting lacquer coated wire.has been found to have excellent insulating qualities, adequate for manycommercial uses, when only a single coat of such gelable lacquer isapplied. The wire may be produced commercially in this manner withoutbaking and at speeds even ten times or more faster than is possible bywire-enameling procedures heretofore known. Uniformly coated wire may bethus produced without skilled attention, and the coating operation maybeSlOwed or even completely stopped without deleteriously affecting thequality of the applied coating.

The gelable lacquers referred to herein are known to the chemicalindustry as such, or sometimes, as gel lacquers or gelation lacquers.They are solutions of complex organic compounds, usually in the categoryof synthetic resins or plastics, which are fluid at moderately elevatedtemperatures (usually in the range of 120 to 200 F.) and solidify to anon-flowing selfsupporting state by gelation upon cooling to atemperature below F. (usually near ordinary room temperature-about 70F). These gelable lacquers as such do not constitute a part of ourpresent invention. Lacquers in which a cellulose ester is the soluteconstituent are being and have been developed. For example, UnitedStates patents to Fordyce et al. Nos. 2,319,051 through 2,319,055,describe gelable cellulose ester lacquers which are fluid attemperatures above F. but form self-supportin non- .flowi g gels whenthe temperature is lowered to 3 below 100 F., and usually to about 70 F.or below. Our invention contemplates using such heretofore knownlacquers, including those described in the above-noted patents andothers as well, in the production of insulated magnet wire by our novelprocedures and in our novel apparatus.

G'clable lacquers have heretofore been emlacquer can run back into thebody of the hot solution. The rate of withdrawal is usually about oneinch every six to twelve seconds, amounting to a linear speed of about0.4 to about 0.8 foot per minute. This slow withdrawal rate is necessarybecause gelable lacquers in the liquid state are characterized by havinga high viscosity, and an excessively thick and irregular accumulation oflacquer is formed on the article if it is withdrawn more rapidly. Uponcooling to a temperature below the critical gelation temperature, the

lacquer sets in the form of a thick coating about 0.006 to about 0.030inch in thickness. Although the thick lacquer coating may be gelled bycooling to a non-flowing state very quickly after removal of the articlefrom the hot lacquer solution, the coated article must be allowed to dryfor ten to twenty minutes or longer before the coating is sufiicientlyhard to withstand moderate handling; and in order for the coating to behard enough to withstand the handling incident to normal use, it must beallowed to dry for a much longer time (usually a matter of hours).

Although the characteristics of the dip-coating procedures heretoforeknown for coating articles with a gelable lacquer, and thecharacteristics of the coatings so produced, have indicated that suchprocedures could not be used in the insulation of magnet wire (whichmust be with drawn from the coating bath at a linear speed far in excessof that used in dip coating articles,

and which must be handled by mechanical supports within an extremelyshort time interval after the wire is withdrawn from the coatingsolution), we have found it possible nonetheless to use such gelablelacquers to produce wholly satisfactory insulated wire.

We have found that when magnet wire is provided with such a coating of agelable lacquer having a thickness less than 0.005 inch, andadvantageously about 0.000l to about 0.002 inch. the applied hot lacquercoating may be cooled to its gelation temperature and substantiallycomplete evaporation of the lacquer solvent may be effected duringpassage of the wire at a relatively high speed from the coating bath tothe first wire-supporting element positioned a reasonable distance fromthe bath. Contact of the coated wire with a supporting element such as apulley wheel or sheave may be made safely without damaging the coatingin about 1.5 minutf s or less, and down to 0.075 minutes when fine wiresare being coated, after application of the coating. By the end of thisperiod the lacquer has gelled and the solvent has evaporated to such anextent as to permit such handling of the wire. The coated wire may bewound upon a spool or in the form of an electrical coil within about0.15 to 3 minutes after the wire passes through the coating solution,the actual time depending more or less on the size of the wire.

In any practical wire-coating operation, the linear speed of the wireimplicit in the time figures given above is such that the coatingthickness specified (less than 0.005 inch) is much less than can beobtained simply by drainage of the lacquer at its natural flow rate fromthe moving wire as it emerges from the lacquer bath.

Based on the foregoing findings, the method of our invention involvespassing a wire beneath the surface of a body of gelable lacquermaintained at above its gelation temperature, limiting the thickness ofthe lacquer film remaining on the wire upon its withdrawal from the bodyof lacquer to less than that obtainable by the natural fiow rate of thelacquer, and cooling the lacquer film on the wire to below its gelationtemperature promptly upon withdrawal of the wire from the body oflacquer. It is generally advantageous, and in many cases possible, toregulate the thickness of the lacquer film so that normal magnet wireinsulation is provided in a single pass of the wire through the body oflacquer. The rate at which the wire is passed through the body oflacquer is, in accordance with the invention, enormously greater thanthe rate at which gelable lacquers may be applied as dip coatings by theprocedures heretofore known, and may even exceed by a substantial marginthe rate at which magnet wires can be enameled by wireenameling methodsknown heretofore. It is also possible to coil wire coated in accordancewith the invention much sooner after application of the coating than hasbeen possible in the production of magnet wires by heretofore knownenameling methods. 1:

Apparatus for producin magnet wire in accordance with the inventioncomprises basically a lacquer vessel, means for heating a body ofgelation lacquer in said vessel to above its gelation temperature, acooling zone maintained at a temperature below the gelation temperatureof the lacquer, and means for continuously passing a wire to beinsulated first through the body of lacquer and therefrom through thecooling zone. The same vessel which contains the lacquer advantageouslyalso defines the cooling zone. In such an arrangement, the body oflacquer is 'in the lower portion of the vessel, and is heated therein toabove its gelation temperature by heating coils or otherwise. In theupper portion of such vessel, above the surface of the lacquer, coolingcoils or other cooling means are provided to maintain the temperature ofthe atmosphere below the gelation temperature.

The foregoing and other features of the invention are described below insome detail, with reference to the accompanying drawings, in which 7Fig. 1 is a cross section through apparatus for producing wire inaccordance with the invention; Fig. 2 is a'view on an enlarged scale ofthe grooved rotatable wheels shown in Fig. 1, taken substantially alongthe line 22 of Fig; 1; j Fig. 3 is a semi-logarithmic plot showing thlinear speed at which wires of different sizes may be coated byenameling methods heretofore commercially employed compared with themethod of the invention;

Fig. 4 is a semi-logarithmic plot of the time within which wires ofdifferent sizes, enameled by heretofore known commercial methods, may be'ing means.

coiled after application of the enamel, compared with the time withinwhich wires coated in accordance with the invention may be coiled;

Fig. 5 is a schematic cross section through a modified form of theapparatus shown in Fig. 1; and r Fig. 6 is a schematic cross sectionthrough another modified form of the apparatus shown in Fig. 1.

The apparatus shown in Figs. 1 and 2 comprises a vessel l0 containing abody of gelable lacquer solution II. A spiral heating coil [2 immersedin the solution is provided to maintain the lacquer at above itsgelation temperature. An inlet connection l3 and an outlet connection'Mare provided for admission and withdrawal of steam, hot oil or water, orother heating fluid. It i of course evident that various other heatingmeans, such as a heating jacket surrounding the lower portion of thevessel Ill, electrical heating windings inside or surrounding the lowerportion of the vessel, or even a screen-enclosed flame impinging on thebottom of the vessel, or a hot plate on which the vessel rests, mayserve as the heat- The temperature at which the gelable lacquer ismaintained by the heating means advantageou -1y is thermostaticallycontrolled.

The normal surface level of the fluid gelation lacquer is well below thetop of the vessel l0. Cooling coils [6 are arranged in the upper portionof the vessel 1 I] to cool the atmosphere in the cooling zone I! (abovethe surface of the lacquer) to a temperature below the gelationtemperature of the lacquer. This cooling zone not only serves to coolthe lacquer coating on the wire to its gelation temperature, but alsoserves to condense the lacquer solvent vapor emanating from the body ofheated lacquer solution, so as to assist (by gravity return to thesolution of the condensed solvent vapor) in maintaining the compositionof the solution. An inlet I 8 and outlet |9 provide for the admissionand withdrawal of cooling water or other cooling fluid to and from thecooling coils l6. As in the case of the heating coil l2, many otheralternatives to the cooling coils l6 shown in the drawings may beprovided for maintaining the temperature in the zone I! at the propervalue. In some cases, where room temperature is safely below thegelation temperature, no special provision for cooling need be made,other than to insure that the wire comes to the temperature of the roomatmosphere.

A wire 2!! to which a lacquer coating is to be applied is drawn from aspool 2i mounted at the side of the vess l 50. A freely rotatable idlerwheel or roller 22 directs the wire from the spool 2| downwardly intothe vessel and into the lacquer solution H. The wire passes around oneof a pair of freely rotatable periph rally grooved wheel 23 and 24.These wheels are mounted so that they project a short distance into thebody of lacquer I I, and the wire is coated with lacouer in the courseof its passa e th rearound. The

grooves in the wheel peripheries define an o ening, between theirabutting faces through which the coated wire 25 emerges from the lacquerinto the cooling zone I1.

From the cooling zone the coated wire passes around one or morewire-supporting pulleys 26 to a capstan 21. Conventional motive meansare provided to rotate the capstan and draw the wire from the spool 2|continuouslythrough the lacquer and thence through the cooling zone. Thewire passes from the capstan to a traverse mechanism 28 which feeds itback and forth across 6 the face of a. spool or other coll form29-mounted on the spindle 30 of a suitably. driven coiling head.

The arrangement of the peripherally grooved wheels 23 and 24 is shown onan enlarged scale .in Fig. 2. Each of these wheels is freely rotable onshort axles 3 l and 32, respectively. Collars 33 on the outer ends ofthe axles bear against the hubs '34 of the wheels and hold them inposition. One

of the wheels 23, preferably that around which the wire 20 passes, ismounted on an arm 35 depending from a bracket 36 and rigidly connectedthereto. The other wheels 24 is mounted on a similar depending arm 31,but one which is pivotally mounted on the bracket 36 by a pivot pin 38.A tension spring 39 urges the pivoted arm 31 and the wheel 24 carriedthereby toward the mating wheel 23, so that normally the peripheries ofthe two wheels abut.

Each of the wheels is formed with a peripheral groove 49, so that anopening 4| is defined at the abutting peripheries of the wheels. It isthrough this opening that t e coated. wire 25 emerges to pass into thecooling zone I! of the vessel l0. Since the amount of lacquer thatremains on the wire after its emergence from between the wheels dependson the size of the opening H in relation to the size of the wire, thegrooves 40 should be of such size as to produce the desired thickness ofthe coating film.

Although V-shaped grooves 40 are shown in the drawings, the shape of thegrooves is not critical. The advantage of V-shaped grooves is that aform tool for cutting such grooves to the correct depth is easily made.The grooves may, however, be semi-circular or rectangular in crosssection, or of any other desired shape, provided only that they serve todefine an opening of the proper size through which the wire can passbetween the abutting peripheries of the wheels.

The peripherally grooved wheels 23 and 24, by their action in limitingthe amount of lacquer remaining on the wire upon its withdrawal from thelacquer solution, insure production of an even coating of desiredthickness about the wire. The small amount of flow necessary for thelacquer passing through the rectangular opening 4| to form film of eventhickness about the periphery of the circular wire occurs quite readilyin the short time interval before the lacquer coating gels. It is forthis reason that the shape of the grooves in the wheels 23 and 25 is notparticularly critical. scribed are capab e of applying a uniform coatingof the desired thickness regardless of the linear speed of the wire. Thegrooved Wheels have been found to operate effectively withlacquersolutions at viscosities up to about 300 poises, the maximumencountered in practice, and are capable of applying a coating of thedesired thickness independently oi:- the normal flow rate of the viscouslacquer solution.

W e have found that die plates having simply a hole therein throughwhich the wire is drawn are not particularly satisfactory in coatingwires with gelation lacquers. keep the wire centered at all times in theopening of such die plates, and in consequence such plates generallyremove more lacquer from one side of the wire than from the other.Unless the rate of production is unduly limited the lacquer gels beforeit has an opportunity to flow to the extent necessary to form an evencoating of uniform thickness completely about the periphery of the wire.

The lacquer solution H which fills the lower Grooved wheels of thecharacted de- It is impossible in practice to portionofthe vessel may beany gelable lac- .quer which is fluid at a moderately elevatedtemperature but which gels to a non-flowing selfsupporting solid,without evaporation of the solvent, when the temperature thereof issufficiently lowered. Many lacquers of this character are known, and thepreparation of still others is within the skill of workers in thisfield. Among the lacquers that we have used with success are those inwhich the solute constituent is an ester of cellulose and at least onefatty acid of one to four carbon atoms. Either a single ester such ascellulose acetate, or a mixed ester such as cellulose acetate-butyrateor cellulose acetate-propionate, may be used. Such lacquers are preparedby dissolving the cellulose ester in a suitable solvent, or mixture ofsolvents, in the correct proportions, and heating to a temperature abovethe gelation temperature. Many suitable solvents for gelable celluloseester lacquers are available. For example, gelable cellulose esterlacquers have been prepared using one or more of the following solvents:alkylene dichlorides (e. g. propylene or butylene chloride) aliphaticalcohols, particularly the lower aliphatic monohydric alcoholscontaining five carbon atoms or less (e.g. ethyl alcohol,

isopropyl alcohol, etc.), toluene, benzene, xylene and ,ligroin.

While we have obtained particularly satisfactory results using celluloseester lacquers of the character referred to above and as disclosed inthe aforementioned Fordyce et a1. and other patents relating to suchlacquers, the invention is not limited to the use of cellulose estergelation lacquers. Gelation lacquers in which the solute constituentispolyethylene (polymerized ethylone) have also been used successfully.Gelation lacquers incorporating still other resinous plasticcompositions as the solute, such as polyvinyl chloride, copolymers ofvinyl chloride and vinyl.

acetate, and ethyl cellulose (a polymer prepared by reaction of ethylchloride and cellulose), may also be employed in accordance with theinvention.

We have obtained excellent results using a gelable lacquer compositioncomposed of about 18% cellulose acetatebutyrate, 16.4% isopropanol and65.6% commercial xylol. This lacquer had a viscosity between 900 and1000 centipoises at 122 F. and a gelation temperature of about 70 F. Thelacquer was maintained at a temperature between 140 and 160 F. in thevessel !0, although the lacquer could be maintained at a highertemperature up to that at which bubbling occurs (usually about 200 F.).wires, meeting or exceeding the specifications established forcommercial enameled magnet wires, have been obtained by passing baremetallic wire through this lacquer solution, in the apparatus describedabove, at speeds ranging from '75 to 160 feet per minute. Equallysatisfactory results are ,obtained using a cellulose acetate gelablelacquer composed of about 1'7 cellulose acetate, about 58% propylenechloride, and about 25% isopropyl alcohol; and using a celluloseacetate-propionate lacquer composed of about 20% celluloseacetatepropionate, 24% isopropyl alcohol, and 56% toluene.

We have also coated magnet wires in accordance with the invention with agelable lacquer solution composed of 20% to 23% of an ethyl celluloseobtained on the market as standard SO-centipoise, medium ethoxy ethylcellulose dissolved in commercial xylol. This lacquer solution wasmaintained at a temperature of about Excellent coated 200 F. in thevessel l0 and'had' a gelation temperature of about 70 F. Similar ethylcellulose gelable lacquers were used in which the solvent was modifiedby the addition of a low boiling range aliphatic hydrocarbon solventhaving a boiling range of 230 to 280 F. We have also modified thephysical characteristics of coatings produced by such lacquers, byincorporating in the lacquer solution agents such as the Paraplex resins(copolymers of sebacic acid, glycerol," and ricinoleic acid).

We have in addition produced very satisfactory coated magnet wires bythe process of the invention using a gelable polyethylene lacquercomprising, as far as we have been able to ascertain, about 20%polyethylene solids in toluol 'as a solvent. The lacquer was applied tothe wire at a temperature of about 180 to F.

Plasticizers may be incorporated in the gelable lacquer solutions, butgenerally, for Wire coating purposes, it is preferable to omit theplasticizer. Unplasticized cellulose ester films deposited on wires inaccordance with the invention are usually harder and more abrasionresistant than plasticized films, and yet are adequately flexible forthe uses to which magnet wires are ordinarily put.

Colored and opaque coatings of gel lacquers can be produced by adding tothe lacquer soldtion an appropriate dye or pigment which is compatibletherewith. The dye should be soluble in the lacquer solution, and manysuch dyes 'are known which do not deleteriously affect the dc"- sirablecharacteristics of the gelled lacquer film on the wire. Pigments andother solid materials such as finely divided aluminum oxide, titaniumdioxide, silicon dioxide, iron oxide, and the like, may be used as thecoloring or opaquing agent. By appropriate choice of the pigment and theamount thereof used in the lacquer, it is possible to modify othercharacteristics of the coating besides its color or opacity. Forexample, a suf' ficient amount of a metal oxide pigment'in the coatingwill generally increase its resistance to heat.

In carrying out the method of our invention in apparatus such as thatshown in Figs. 1 and 2, the wire 20 is drawn continuously from the spool21 around the grooved wheel 23, whereby it is immersed in the body oflacquer ll. As the result of such immersion, the hot liquid lacquer wetsand adheres to the surface of the wire. The temperature of the lacqueris maintained by the heating coils at above the gelation temperature andhigh enough to establish the desired lacquer viscosity, but preferablynot so' high that bubbles form in the solution (ordinarily bubbleformation begins about 200 F. or higher). The wire is drawn upwardlythrough the opening ll defined by the grooves in the abuttingperipheries of the freely rotatable wheels 23 and 24, ro-

tation of which is caused by the movement of the wire.

The opening 4| limits the thickness of the film of lacquer remaining onthe wire after it has passed therethrough to less than could be obtainedby the natural flow rate of the lacquer with the wire travelin at anyreasonable coating speed. As the coated wire emerges from the opening4!, the coating remains liquid for just about long enough to flow intoand form a uniform coating about the wire, and it then solidifies bygelation to form a self-supporting film on the Wire.

In coating wire with a gelable cellulose acetate-butyrate lacquermaintained at a coating temperature of about 140 to 160 R, we. havefound that gelation and solvent evaporation take place satisfactorily inthe cooling zone I! without the aid of cooling by the cooling coils. Theatmosphere at ordinary room temperature suffices to accomplish theseresults. However, improved gelation and, more particularly, improvedsolvent recovery by condensation of solvent vapor in the cooling zonel1, have been obtained by lowering the temperature of the cooling zoneI! to below room temperature by the use of cold tap water circulatingthrough the cooling coils.

Whether or not the cooling coils are used to cool the zone I! to belowroom temperature,

gelation and solvent evaporation take place so rapidly that, with thewire moving at normal coating speeds, the coated wire can be touchedlightly with the fingers without damage to the film at a point about 2or 3 feet above the top of the vessel It. Solvent evaporation continuesas the coated wire 25 travels toward the sup portin pulley 26, and bythe time the wire reaches it gelation is complete and solventevaporation has advanced to the point that the coated wire may be passedover the pulley without damage to the coating film. In general, forordinary coating speeds, a distance of about 15 feet between the groovedwheels 23 and 24 and the upper pulley 26 is sufiicient to permit quitecomplete hardening of the coating. This distance may of course bevaried, if desired, depending upon the wire size and coating speed andthickness. For example, in coating fine wires such as No. 37 A. W. G., adistance somewhat less than 15 feet is usually sufficient, whereas withrelatively coarse wires such as No. 15 A. W. G. a somewhat greaterdistance may be preferable, particularly if a thick coating of thelacquer is applied. By establishing a distance between the upper pulley26 and the capstan 21 approximately equal to the distance between theupper pulley 26 and the grooved wheels 23 and 24, the coatin film willbe sufliciently hard to withstand the distortion caused by the capstanand by the coiling operation, which may follow immediately.

Wires of any size may be coated by the method and apparatus of theinvention. In the case of the larger wires, such as No. 14 to No. 20 A.W. G., the rate of solvent evaporation from the gelled coating may beincreased by gently heating the coating on the wire over a portion ofthe distance between the top of the vessel I and the upper pulley 26.Such heating may be accomplished by passing the wire through a steamcoil, or by infra-red heating lamps, or in any other desired manner.

As pointed out above, the linear speed with which wires can be enameledin conventional enameling ovens depends on the size of the wire; and thesame is more or less true in coating wires in accordance with theinvention. The coating speeds involved in the method of the inventionare indicated in Fig. 3 of the drawings, wherein coating speeds in feetper minute are plotted against the size (A. W. G.) of the wire beingcoated. The line ab on Fig. 3 indicates substantially the maximum linearspeed with which it has been possible heretofore to enamel wires incommercial practice with oleo-resin enamels requiring baking. Animportant commercial advantage of the new method is that it permitscoating to proceed at a much higher linear rate of travel of the wire.The .line c.d

of Fig. 3 indicates a rair. averagenormal coating speed for coatingwires of different sizes in accordance with the invention, although inparticular cases a somewhat. lower or substantially higher coating speedmay be preferable; and. the line e--,f is indicative of speeds thatactually have been attained in some cases. Ordinarily commercial wirecoating in accordance with the invention will be conducted at speeds atleast about double thosev attainable in baking-enamel coatingoperations. If the linear rate of withdrawal of articles being coated bythe dip methods heretofore known for applying elable lacquers wereplotted to scale on Fig. 3, the speed of application of such thincoatings as are re.- quired for magnet wire insulation would lead to acurve that would be. virtually indistinguishable from the Wire Size axisof the plot. It is evident from this plot that wires can be coated inaccordance with the invention much more rapidly than with enamels thatrequire baking (i. e., they can be coated at a rate in excess of therate shown by the line ab of Fig. 3), and enormously more rapidly thanwould be possible by heretofore known dip methods.

Related to the high coating speed attainable is the very short time thatneed. elapse. between applying the lacquer and coiling a wire coated in.accordance with the invention. Coiling may be either on spools forconvenience in handling, or in the form of finished electrical coils forthe electrical industry. Fig... i isa plot, against wire size, of thetime elapsed between, application of the coating and coiling of thewire. in the cases (1) of wires, coated accordance with the inventionand. (2) in accordance with here tofore known commercial methods. Thevline g-h of Fig. 4, indicates the minimum time int-h..- in which wiresof .difierent sizes may he coiled commercially after coating with.oleoresin enamels and baking. The elapsed time between immerson of anysection of the wire in the lacquer and coiling of said section may, inaccord: ance with the invention,v be less than that indicated by theline gh. The line of Fig. .1 indicates; a, ,fair; average, time to allowin. ordinary cases between. application of. lacquers. in accordancewith. the invention and ceiling of the coated wire. It is clear fromthis pilot that wire coated. in accordance with the inventionrnay becoiled much sooner aftera-pplication of the coat.- ing composition thanis the case in the. commercial wire-enameling procedures heretoforeknown. The short time interval between coating andcoileing that isattainable in accordance with the invention may be contrastedwith thetime. of several hours required for drying and hardening the thickgelable lacquer coatings formed by heretofore known dipping methods ontool nan-.- dles and other such articles.

The line m-n plotted on Fig. e indicates the very short time, intervalthat need elapse lee..- tween application of the enamel andv passage. ofthe coated wire over the. first supporting p111- ley .or sheave. afteremergence of the wire from the body .of lacquer. Within this period oftime the lacquer may be gelled and suiiicientv solvent evaporated toproduce a hard enough coating to withstand the forces to which it issubjected in being drawn over the support. In general the normal maximumelapsed time between the passage of any section of the wire through thelacquer and passage of the same section over the supporting sheave isless than about 3.5 minutes, and in the case of .finev wires (say No. 40A. W. .G.)

it may be only 4.5 seconds (0.075 minute) or less.

As hereinbefore stated, wire prepared in accordance with the inventionmay be wound into finished electrical coils directly after coating, as alast step in a conjoint wire-coating and coilwinding operation. Thisrepresents the fulfilment of a desire that has long been felt in themagnet wire industry, but one that previously has not been attainedbecause of the limitations imposed by the wire-enameling proceduresheretofore commercially available. In winding electrical coils it isgenerally necessary from time to time to start and stop the movement ofwire to the coil winder, and sometimes to vary the linear speed of wiretravel. It is not feasible to interrupt the passage of wire through anenameling oven, or vary the speed with which it passes through the oven,for the reasons already given. Furthermore, it is not economicallypractical to limit coil winding to the speeds attainable in producingbaked-enamel coated wires, or to subject it to the production hazardsincident to breakage of the wire during the course of the coatingoperation. Our new wire coating method is not subject to theselimitations. The coating speeds attainable are commensurate withcommercial coil winding speeds, and passage of the wire through the bodyof gelable lacquer may be slowed down or speeded up, or even stoppedaltogether, as the occasion to do so arises, without deleteriouslyaffecting the thickness or quality of the coating on the wire. Whereasan interruption in the passage of wire through a commercial wireenameling oven almost invariably results in ruining the wire, aninterruption in the new coating operation has no significant effect onthe wire, and the passage of the wire through the gelable lacquer may beresumed after an interruption without discarding any portion of thewire.

Various modifications may be made in the method and apparatus describedabove. For example, in producing wires with fairly thick coatings, itmay be desirable to modify the apparatus as shown in Fig. 5. Thismodification involves providing an'idler pulley or sheave '42 below thefirst pulley 26 over which the wire passes after emerging fromthelacquer, and a second idler 43 about at the elevation of the firstpulley 26. The coated wire passes upwardly around the first pulley 26,downwardly and around the idler 42, and thence upwardly and around thesecond idler 43 to the capstan 21. The extra wire path length providedin this modification between the coating bath and the capstan allows, ata given wire speed, some additional time for solvent evaporation, inthose cases where such is desirable.

It is ordinarily possible and desirable to apply a coating of adequatethickness to provide normal magnet wire insulation in a single pass ofinitially bare wire through the body of gelable lacquer. Coatingthicknesses between 0.0001 inch and 0.002 inch are quite easily producedin accordance with the invention in a single pass through the lacquer,and thicknesses in this range (commonly near 0.0005 inch) are thoseusually desired for magnet wire insulation. Hence a feature of theinvention is that in many cases the wire may be packaged for theelectrical trade (either as a spool or coil of. wire for convenienthandling, or as a finished electrical or magnet coil) after but a singlepass through the gelable lacquer coating solution.

For some purposes magnet wires havingcoat 12 ings up to 0.005 inch aredesirable, and for producing such wires apparatus modified as shown inFig. 6 may be used with advantage. In this modification a second set ofcoating rollers 44 and 45, similar to the first set of rollers 23 and 24described above, is mounted in the vessel ID at the gelable lacquersurface. A second supporting pulley or sheave 46 similar to the firstsuch pulley 26 also is provided. The incoming wire 28 passes down andthrough the body of gelable lacquer, around one of the rollers 24, andup to and around the supporting pulley 26. Thence the wire passes againinto the body of lacquer and around a roller 34 of the second set to thesecond supporting pulley 46, from which it passes to the capstan 21.Thus two coats of the lacquer are applied to the wire in a singleoperation. We have found that a considerable number of coats may beapplied thus directly after gelation of the previous coat, withoutinjuring the coat or coats previously applied. There is no advantage, sofar as insulating magnet wires are concerned, however, in applying morethan two coats. We have been able to develop coating thicknesses up to0.016 inch in only two passes of the wire through the lacquer, and sotwo coats may be regarded as the maximum necessary forordinary wirecoating operations even in those cases Where thicker-than-usual coatingsare desired.

Magnet wire produced in accordance with the invention is the equal ofconventional enameled magnet wire in many respects, and it is superiorin some respects. For ,example, magnet wire comprising a metallicconductor having thereon a thin, substantially continuous insulatingfilm of an ester of cellulose and one or more fatty acids containing oneto four carbon atoms (e. g. cellulose acetate-butyrate) applied directlyincontact with the conductor surface, easily passes the qualityacceptance tests established for ordinary enameled wire. The celluloseester coating possesses high abrasion resistance. It is substantiallyinsoluble in and not appreciably softened by petroleum oils, water orother liquids to which it is likely to be exposed in service. The wiremay be bent on a mandrel of its own diameter without cracking thecoating, even when the coating is unplasticized. The insulationresistance is high, even after prolonged exposure at a temperature of120 F. to an atmosphere saturated with water vapor. The dielectricstrength is likewise high. Continuity of the film is substantially equalto that of ordinary enameled wire. The Q value of coils wound from thenew wire generally is substantially higher than that of coils wound fromordinary enameled wires. (The Q value of an electrical coil indicatesthe magnitude'of the ratio of the amount of energy stored in the coil tothe amount of energy dissipated therein for cycle of an alternatingcurrent flowing therethrough. A high Q value, which indicates that thecoil will dissipate only a small amount of the power supplied to it orpassed through it, is much desired in magnet wire coils employed inradio circuits and other fairly high frequency alternating currentdevices.)

Another feature of wires coated with a gelable lacquer in accordancewith the invention is the ease with which the coating may be removedfrom the wire. for making electrical connections. For example, theinsulation may be removed readily from wires coated with a celluloseacetate-butyrate gel lacquer by dipping the wire in acetone. This leavesa clean wire surface to which electrical connections may easily be madeby soldering or otherwise. This is an outstanding advantage of the gellacquer coated wire over baked enamel coated wire from which the enamelcan be removed only by scraping or by the use of an abrasive such asSandpaper, or by powerful solvents. Sandpapering is slow and frequentlycauses breakage of fine Wires, and the solvents which will removeheretofore known baked enamels are expensive, toxic, must be handledcarefully and must be thoroughly washed from the wire.

Coatings applied to wires in accordance with the invention do not adhereto the wire as do baked enamel coatings, but this is not a disadvantage,and is even an advantage in that it permits easy mechanical stripping ofthe coating if a suitable solvent is not at hand. Solvent evaporationthat ensues after gelation of the coating is accompanied by shrinkage ofthe coating tightly about the wire, so that there is no danger of thecoating slipping on the wire accidentally.

It is evident from the foregoing that the invention provides a magnetwire possessing in a large measure the properties desired in such wires,and yet that can be madeby the method and with the apparatus of theinvention much more rapidly and with much less costly equipment thanheretofore known enameled wires.

We claim:

1. The method of producing insulated magnet wire which comprises passinga wire through a body of gelable lacquer which i maintained atsubstantially atmospheric pressure and which is maintained in the liquidstate by being heated to above its gelation temperature, withdrawing theWire from the body of lacquer and substantially simultaneously limitingthe thickness of the lacquer film on the wire to less than 0.005 inchand less than that obtainable by the natural flow rate of the lacquer bypassing the wire through a restricted opening formed by two arcuate membrs, at least one of which rotates in a direction such that its edgeadjacent the wire moves in thesame direction as the movement of the wirethrough the opening, and cooling the lacquer film on the wire to belowits gelation temperature promptly upon withdrawal of the wire from therestricted opening.

2. The method of producing insulated magnet Wire which comprises passinga wire through a body of gelable lacquer which is maintained atsubstantially atmospheric pressure and which is maintained in the liquidstate by being heated to above its gelation temperature, withdrawing thewire from the body of lacquer and substantially simultaneously limitingthe thickness of the lacquer film on the wire to less than 0.005 inchand less than that obtainable by the natural flow rate of the lacquer bypassing the Wire through a restricted opening formed by two arcuatemembers at least one of which rotates in a direction such that its edgeadjacent the wire moves in the same direction as the movement of thewire through the opening, and cooling the lacquer film on the wire tobelow its gelation temperature promptly upon withdrawal of the wire fromthe restricted opening, the rate of passage of the wire through the bodyof lacquer and through the restricted opening in relation to the size ofthe wire being at least about equal to the rate shown by the line c-d ofFig. 3 of the accompanying drawings.

' lacquer by passing the wire through a restricted opening formed by twoarcuate members at least one of which rotates in a direction such thatits edge adjacent the wire moves in the same direction as the movementof the wire through the opening, cooling the lacquer film on the wire tobelow its gelation temperature promptly upon withdrawal of the wire fromthe restricted opening, and winding the wire into an electric coil ofdesired size and shape directly after gelation of the lacquer coatingand as the final step in a conjoint wire-coating and coil-windingoperation.

4. The continuous method of producing a coil of insulated wire whichcomprises passing a me tallic wire through a body of gelable lacquerwhich is maintained at substantially atmospheric pressure and which ismaintained in the liquid state by being heated to above its gelationtemperature, withdrawing the wire from the body of lacquer andsubstantially simultaneously limiting the thickness of the lacquer filmremaining on the wire to less than 0.005 inch and less than thatobtainable by the natural fiow rate of the lacquer by passing the wirethrough a restricted opening formed by two arcuate members at least oneof which rotates in a direction such that its edge adjacent the wiremoves in the same direction as the movement of the wire through theopening, cooling the lacquer film on the wire to below its gelationtemperature promptly upon withdrawal of the wire from the restrictedopening, and winding the wire into a coil of desired size and shapedirectly after gelation of the lacquer coating and as the final step ina conjoint wire-coating and coiling operation, the elapsed time betweenimmersion of any section of the wire in the body of lacquer and coilingof said section, in relation to the size of the wire, being notappreciably greater than the time shown by the line a'-lc of Fig. 4 ofthe accompanying drawings.

HARRY L. SAUMS.

JOHN H. VAIL.

HOWARD W. STURGIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 862,935 Pfanstiehl Aug. 13, 19071,531,259 Turner Mar. 24, 1925 1,993,838 Hagedorn Mar. 12, 19352,044,970 Candy June 23, 1936 2,051,944 I-Iershberger Aug. 25, 19362,156,607 Schon May 2, 1939 2,197,622 Sendzimir Apr. 16, 1940 2,291,670Wiley Aug. 4, 1942 2,308,638 Balthis Jan. 19, 1943 2,315,645 Newton Apr.6, 1943 2,350,742 Fordyce June 6, 1944

3. THE CONTINUOUS METHOD OF PRODUCING AN ELECTRIC COIL WHICH COMPRISESPASSING A METALLIC WIRE THROUGH A BODY OF GELABLE LACQUER WHICH ISMAINTAINED AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND WHICH IS MAINTAINEDIN THE LIQUID STATE BY BEING HEATED TO ABOVE ITS GELATION TEMPERATURE,WITHDRAWING THE WIRE FROM THE BODY OF LACQUER AND SUBSTANTIALLYSIMULTANEOUSLY LIMITING THE THICKNESS OF THE LACQUER FILM REMAINAING ONTHE WIRE TO LESS THAN 0.005 INCH AND LESS THAN THAT OBTAINABLE BY THENATURAL FLOW RATE OF THE LACQUER BY PASSING THE WIRE THROUGH ARESTRICTED OPENING FORMED BY TWO ARCUATE MEMBERS AT LEAST ONE OF WHICHROTATES IN A DIRECTION SUCH THAT ITS EDGE ADJACENT THE WIRE MOVES IN THESAME DIRECTION AS THE MOVEMENT OF THE WIRE THROUGH THE OPENING, COOLINGTHE LACQUER FILM ON THE WIRE TO BELOW ITS GELATION TEMPERATURE PROMPTLYUPON WITHDRAWAL OF THE WIRE FROM THE RESTRICTED OPENING, AND WINDING THEWIRE INTO AN ELECTRIC COIL OF DESIRED SIZE AND SHAPE DIRECTLY AFTERGELATION OF THE LACQUER COATING AND AS THE FINAL STEP IN A CONJOINTWIRE-COATING AND COIL-WINDING OPERATION.